This disclosure relates generally to methods and apparatus for controlling pressure during hydrocarbon production. More specifically, this disclosure relates to methods and apparatus for preventing over-pressurization of equipment during hydrocarbon production.
As hydrocarbon reservoirs of increasingly high pressures are explored and developed, there are increasing demands to improve safety by providing increased control of high pressure fluids. To this end, high integrity pressure protection systems (HIPPS) have been employed in the oil and gas industry to provide a barrier between equipment designed to contain high pressure and equipment that is not capable of containing high pressure. HIPPS conventionally include one or more valves that are actuated by a control system that monitors pressure immediately upstream or downstream of the valves. When the control system senses an excessive pressure, the valves are closed as quickly as possible.
In certain subsea installations partially located on the sea floor, several wellheads, topped with wet trees, are fluidly connected to a single production manifold. The production manifold is in turn fluidly connected to a platform located on the sea surface via a flowline and a riser. The riser, is usually fluidly connected to a flare, a boarding and shut down valve (BSDV), a choke, among other components of a platform receiving system. The wellheads, the wet trees, and sometimes the production manifold coupled thereto, are designed to contain high pressure. But the flowline that couples the production manifold to the riser is rated to a pressure that is lower than the wellheads, but still higher than the flowing pressure. The pressure rating of the flowline is sometimes referred to as derated. A subsea HIPPS, also rated to high pressure, may be employed between the wellheads and the subsea manifold. The HIPPS actuates so as to automatically shut off any flow from the wellheads in response to excessive pressure. Thus the HIPPS contains excessive pressure, avoiding damaging the flowline or other equipment that is not capable of containing high pressure.
To accommodate the time that it will take to close the valves, subsea HIPPS often include a length of “high pressure” flowline designed to contain the increased pressure occurring downstream of the HIPPS until the valves can be closed. The zone equipped with high pressure flowline is referred to as the fortified zone. The length of the high pressure flowline needed and/or the size of the fortified zone are dependent on the operating speed of the HIPPS as well as the expected flow conditions. In certain applications, the length of the high pressure flowline may be several hundred and even several thousand feet long. Accommodating such length of high pressure flowline makes installation of subsea equipment challenging, in particular because of the large, and variable distances between the wellheads and the production manifold that are needed to dispose the required length of high pressure flowline. Also, retrofitting a subsea HIPPS to an existing facility without modifying its layout is usually not feasible.
Thus, there is a continuing need in the art for methods and apparatus for providing increased safety and containment of high pressure in hydrocarbon exploration and production.